Whisk all the dressing ingredients with 3 tbsp olive oil and season. Scrape the seeds out of each pepper half then rub the halves with a little oil. Barbecue, griddle or grill, cut side down, for 5 minutes until the edges are charred and starting to soften. Turn the peppers over, and sit a slice of mozzarella in each half. Cook for another 5-10 minutes until the cheese has melted and the bases of the peppers have softened. If you like your mozzarella crisp, then flash the peppers briefly under the grill. Arrange the peppers on a platter and drizzle with the dressing.